(A) Field of the Invention
This invention relates to coated abrasive products comprising a fabric backing, a resin coating or coatings and abrasive grain embedded in the resin. More particularly, the invention relates to such coated abrasive products for use in heavy duty applications.
(B) History of the Prior Art
In the prior art it has been highly desirable to manufacture coated abrasive products having tear, body and strength as high as is practical. While coated abrasives have been made in the prior art having acceptable tongue tear, body and strength, such characteristics were nevertheless not as high as desired for certain applications. In particular, in heavy duty applications, especially when the coated abrasives involved contain coarse grits (grit size 60 and coarser). One reason for failure of the product occured because of grain shedding and excessive flexing in certain severe grinding operations. Another method of failure in such heavy duty applications as in abrasive belts, is that such coated abrasives do not retain body stiffness for a period as long as desirable. For these reasons, such heavy duty belts fold and then tear or split in the running direction in heavy duty use. Furthermore, such belts in the prior art did not have impact resistance and resistance to thermal stress as high as desirable in either abrasive belts or abrasive discs, and resin coatings would frequently crack which often caused excessive water absorption in the products in wet applications.
It had been known in the prior art that resin sizes could be applied to the back of coated abrasive products which backsizes contained microspheres or microballoons to improve the durability of product in use and to aid in the making of lapped belt joints in the backing. Unfortunately, the incorporation of microspheres in the backsize resin coating did not significantly improve impact resistance and resistance to thermal stress. Furthermore, the improvement in retained body stiffness and tongue tear was not as high as desirable. In addition, there was no significant improvement in cracking of the maker or size resin coating. Such incorporation of microspheres in backsize coatings is disclosed in U.S. Pat. No. 4,111,667.
As used herein, it is understood that "backsize" means a resin coating applied to a fabric backing on the side of the fabric opposite the side upon which abrasive grains are applied. A "size" coating as used herein refers to a frontsize coating which is applied to the fabric on the front of the fabric. The front of fabric refers to that side of the fabric to which abrasive grain is ultimately applied. A "maker coat" means the coating applied to the fabric, whether sized or unsized, which ultimately holds the abrasive grain.